Abstract:
A new model for electrostatic ultrasonic transducers with V-grooved backplates is developed. The model treats the diaphragm of the transducer as a plate supported by an air spring. Since the tension is usually not used and unnecessary, only the bending stiffness of the diaphragm, D, and the air-gap spring stiffness, K, are taken into account. It is revealed by the DK model that the first resonant frequency of the transducer stems from the air-gap spring, like a Helmholtz resonator, and the second resonant frequency corresponds to the first mode frequency of the diaphragm vibrating as a thin plate. The motion of the diaphragm can be described approximately by the combined contributions of the two parts. According to the theory, a wider bandwidth can be obtained by designing the second resonant frequency to be near the first one with an appropriate selection of geometric dimensions and material parameters. For a typical V-grooved transducer with an 8-(mu)m-thick Mylar diaphragm and a 0.5-mm pitch air gap, the first resonant frequency predicted by the model is 50.9 kHz, and the second one is 78.6 kHz. The prediction is consistent with experimental results. [Work supported by Anhui Natural Science Foundation of China.]